The ABS at the time said it had been forced to take the site offline on Census night following a series of DDoS attacks combined with the failure of the network geoblocking function and the collapse of a router.

The statistics body has publicly criticised IBM for failing to properly implement a geoblocking service, which would have halted the international DDoS attack targeted at the Census site.

But IBM is now laying blame squarely at the feet of its internet service provider partner NextGen and NextGen's upstream supplier Vocus for the geoblocking bungle.

It claimed NextGen had provided "repeated" assurances - including after the day's third DDoS attack - that a geoblocking strategy that IBM codenamed 'Island Australia' had been correctly put in place.

However, when the fourth and biggest DDoS attack of the day hit at around 7:30pm, IBM said it became clear that a Singapore link operated by Vocus had not been closed off, allowing the attack traffic to pass through to the Census site.

"Vocus admitted the error in a teleconference with IBM, NextGen and Telstra around 11.00 pm on 9 August 2016," IBM said.

"Had NextGen (and through it Vocus) properly implemented Island Australia, it would have been effective to prevent this DDoS attack and the effects it had on the eCensus site. As a result, the eCensus site would not have become unavailable to the public during the peak period on 9 August 2016."

IBM said while it accepted its responsibility as the head contractor for the eCensus, it could not have avoided using ISPs to provide links for the website.

"It is not possible for an IT services company such as IBM to implement the 2016 eCensus without engaging ISPs. It was necessary for IBM to involve the ISPs in the implementation of the geoblocking solution as they have control over their respective data networks and are in a position to block internet traffic originating from particular domains or IP addresses."

IBM did, however, admit what many security experts speculated had occured - that following the fourth DDoS a system monitoring dashboard showed an apparent spike in outbound traffic, causing its staff to wrongly assume data was being exfiltrated from the website, prompting IBM to shut down the website.

The contractor also revealed that a configuration error meant a manual reboot of one of its routers - which was needed after the eCensus firewall became overloaded with traffic - took much longer to rectify than it should have, keeping the site offline for a further hour and a half.

NextGen, Vocus fight back

But Vocus said NextGen was well aware that Vocus would not provide geoblocking services, and had instead recommended its own DDoS protection.

"If Vocus DDoS protection product was left in place the eCensus website would have been appropriately shielded from DDoS attacks," Vocus said in its submission to the inquiry.

Vocus refuted IBM's claim that it had failed to implement geoblocking, revealing that it had not been made aware of IBM's DDoS mitigation strategy - including 'Island Australia' - until after the fourth attack on August 9.

"As a result, any assumption that Vocus was required to, or had implemented Island Australia or geo-blocking including, without limitation ... are inaccurate," Vocus said.

"Once Vocus was made aware of the fourth DDoS attack, it implemented a static null route to block additional DDoS traffic at its international border routers within 15 minutes."

Vocus also argued that the fourth DDoS was not as large as IBM claimed, comprising of attack traffic that peaked at 563Mbps and lasting only 14 minutes - which it said was "not considered significant in the industry".

"Such attacks would not usually bring down the Census website which should have had relevant preparations in place to enable it to cater for the expected traffic from users as well as high likelihood of DDoS attacks."

NextGen, in its own submission, claimed it had "strongly recommended" to IBM that it take up a DDoS protection product like that on offer by Vocus, but the contractor declined.

The ISP said it was not made aware of details of IBM's 'Island Australia' strategy until six days before the eCensus went live in late July.

At that point it told IBM that an IP address range it had provided was part of a larger aggregate network and therefore would not respond to "specific international routing restrictions" if 'Island Australia' was implemented.

"Nextgen recommended using an alternative IP address range, which would give IBM better control, but this was rejected by IBM," the ISP said.

"Nextgen believes that the individual host routes picked by IBM may not be exhaustive, and DDoS attacks could come from other routes in the IP address range (which they did in the third DDoS attack on Census day)," NextGen said.

"There were a number of routes without geoblocking during the fourth DDoS attack, and which were not identified during testing, along with the [Vocus] Singapore link."

NextGen said it again offered to implement DDoS protection, this time at its own cost, which IBM agreed to four days after the events of August 9.

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